Grey, heavily cratered, and peering out from the black of space, Ganymede looks a lot like our moon. But the icy rock is more than 650 million kilometers (400 million miles) away – it's the largest moon in the Solar System, and it circles Jupiter. NASA's Juno spacecraft has been rocketing around Jupiter since 2016, but on Monday, it zipped past Ganymede, coming within 1,000 km (650 miles) of the moon. No spacecraft had gotten that close in more than two decades – the last approach was NASA's Galileo spacecraft in 2000. In just 25 minutes, Ganymede went from being...